Outer blade cutting wheel and making method

ABSTRACT

In an outer blade cutting wheel comprising an annular thin disc base of cemented carbide having an outer diameter of 80-200 mm, an inner diameter of 30-80 mm, and a thickness of 0.1-1.0 mm, and a blade section disposed on an outer periphery of the base, the blade section comprises diamond grains and/or CBN grains bound with a metal bond having a Young&#39;s modulus of 0.7-4.0×10 11  Pa and has a thickness which is greater than the thickness of the base by at least 0.01 mm. The outer blade cutting wheel is capable of cutting a workpiece at a high accuracy and a reduced allowance, improves machining yields, and reduces machining costs.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No. 13/493,539,filed on Jun. 11, 2012, which is a division of U.S. application Ser. No.12/342,941, filed on Dec. 24, 2008 which is based upon and claimspriority under 35 U.S.C. § 119(a) on Patent Application No. 2007-339212filed in Japan on Dec. 28, 2007, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to an outer blade cutting wheel for cutting rareearth sintered magnets, and a method for preparing the same.

BACKGROUND ART

Outer blade cutting wheels for cutting rare earth sintered magnets aredisclosed in JP-A 9-174441, JP-A 10-175171, and JP-A 10-175172 ascomprising a cemented carbide base having an outer periphery to whichdiamond abrasive grains are bonded with phenolic resins or the like.Since diamond grains are bonded to the cemented carbide base, the baseis improved in mechanical strength over prior art alloy tool steel andhigh-speed steel, leading to a higher accuracy of machining. Also byreducing the thickness of the blade with using a cemented carbide base,the yield of machining can be improved and the machining speed beaccelerated. While these cutting wheels using cemented carbide basesshow better cutting performance than prior art outer blade cuttingwheels, the market poses an increasing demand to reduce the cost ofcutting wheels. It would be desirable to have a novel high-performancecutting-off wheel overwhelming the prior art outer blade cutting wheels.

While various cutting techniques including outer blade cutting-off,inner blade cutting-off and wire saw cutting-off techniques areimplemented in machining rare earth permanent magnets or sinteredmagnets, the outer blade cutting-off technique is most widely employed.By virtue of many advantages including an inexpensive cutting wheel, anacceptable cutting allowance on use of hardmetal blades, a highaccuracy, a relatively high machining speed, and a mass scale ofmanufacture, the outer blade cutting-off technique is widely employed incutting of rare earth sintered magnets.

Traditional cutting wheels for outer blade cutting used bases made ofsteel alloy materials such as alloy tool steels (e.g., SKD grade in JIS)and high-speed steels in the art. However, JP-A 9-174441, JP-A10-175171, and JP-A 10-175172 (the inventors including the same as thepresent) disclose cutting wheels using bases of cemented carbides.Cemented carbides made by cementing tungsten carbide (WC) grains in abinder matrix of cobalt or nickel metal by sintering are robustmaterials having a Young's modulus as high as 450 to 700 GPa andextraordinarily stronger than the steel alloy materials having a Young'smodulus of the order of 200 GPa.

A high Young's modulus implies that the quantity of deformation of ablade under a cutting force (or cutting resistance) is reduced. This, inturn, implies that under the same cutting force, the deflection of theblade is reduced, and that for the same deflection of the blade, thesame accuracy of cutting is possible even when the thickness of theblade is decreased. Although the cutting force applied per unit area ofthe blade remains substantially unchanged, the overall cutting forceapplied to the blade becomes smaller by the thickness decrease. In themultiple machining process where a magnet block is machined intomultiple pieces at a time by a cutter assembly comprising a multiplicityof cutting wheels, the total cutting force applied to the cutterassembly is reduced. This allows the number of cutting wheels to beincreased for a motor of the same power, or the cutting force to bereduced for the same number of cutting wheels, leading to a saving ofthe motor power. If the motor power has a margin relative to the cuttingforce, the advance of the cutting wheel assembly may be accelerated toshorten the cutting time required.

The use of high-modulus cemented carbide bases considerably improved theproductivity of outer blade cutting. However, the market imposes an everincreasing demand on rare earth sintered magnets, with manufacturersentering into keen competition toward cost reduction. For effectiveutilization of rare earth permanent magnet material, the smaller thecutting allowance, the higher becomes the material utilization yield.The higher the machining speed, the more is improved the productivity.It would be desirable to have an outer blade cutting wheel which offersa high modulus and high accuracy despite a reduced thickness of bladerelative to the current cemented carbide base cutting wheels.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide an outer blade cutting wheelwhich is capable of cutting at a high accuracy and a reduced allowancewhile achieving improved machining yields and reduced machining costs,and a method for preparing the same.

The invention relates to an outer blade cutting wheel comprising a basemade of cemented carbide. A metal bond having a higher strength andhigher modulus is used to bind abrasive grains comprising diamondgrains, CBN grains or a mixture of diamond grains and CBN grains to theouter periphery of the base, thereby improving the mechanical strengthof the blade section and the overall mechanical rigidity of the outerblade cutting wheel. The invention thus succeeds in reducing thethickness of the blade section and accelerating the cutting speed.

In one aspect, the invention provides an outer blade cutting wheelcomprising a base in the form of an annular thin disc of cementedcarbide having an outer diameter of 80 to 200 mm defining an outerperiphery, an inner diameter of 30 to 80 mm defining a bore, and athickness of 0.1 to 1.0 mm, and a blade section disposed on the outerperiphery of the base and comprising abrasive grains bound with a metalbond, the abrasive grains comprising diamond grains, CBN grains or amixture of diamond grains and CBN grains, the metal bond having aYoung's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa, the blade section having athickness which is greater than the thickness of the base by at least0.01 mm.

In a preferred embodiment, the metal bond has a Vickers hardness of 100to 550 and a density of 2.5 to 12 g/cm³. Typically, the metal bondcomprises at least one metal selected from the group consisting of Ni,Fe, Co, Cu, and Sn, an alloy comprising at least two of the foregoingmetals, or an alloy comprising at least one of the foregoing metals andphosphorus.

In a preferred embodiment, the blade section is formed by electroplatingthe metal bond so that the metal bond is deposited on the outerperiphery of the base while binding the abrasive grains therewith. Morepreferably, the metal bond as deposited on the base by electroplatinghas an internal residual stress between −2×10⁸ Pa and 2×10⁸ Pa.

In another preferred embodiment, the blade section is formed by brazingthe abrasive grains so that the metal bond is affixed to the outerperiphery of the base while binding the abrasive grains therewith.

In a second aspect, the invention provides a method for preparing anouter blade cutting wheel comprising providing a base in the form of anannular thin disc of cemented carbide having an outer diameter of 80 to200 mm defining an outer periphery, an inner diameter of 30 to 80 mm,and a thickness of 0.1 to 1.0 mm; and electroplating a metal bondtogether with abrasive grains to deposit on the outer periphery of thebase an electroplated layer in which the abrasive grains are bound withthe metal bond, the abrasive grains comprising diamond grains, CBNgrains or a mixture of diamond grains and CBN grains, the metal bondhaving a Young's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa, the electroplatedlayer having a thickness which is greater than the thickness of the baseby at least 0.01 mm and serving as a blade section. Preferably, themetal bond as deposited on the base by electroplating has an internalresidual stress between −2×10⁸ Pa and 2×10⁸ Pa.

In a third aspect, the invention provides a method for preparing anouter blade cutting wheel comprising providing a base in the form of anannular thin disc of cemented carbide having an outer diameter of 80 to200 mm defining an outer periphery, an inner diameter of 30 to 80 mm,and a thickness of 0.1 to 1.0 mm; and brazing abrasive grains with ametal bond onto the outer periphery of the base to form a layer in whichthe abrasive grains are bound with the metal bond, the abrasive grainscomprising diamond grains, CBN grains or a mixture of diamond grains andCBN grains, the metal bond having a Young's modulus of 0.7×10¹¹ to4.0×10¹¹ Pa, the layer having a thickness which is greater than thethickness of the base by at least 0.01 mm and serving as a bladesection.

In a preferred embodiment, the metal bond has a Vickers hardness of 100to 550 and a density of 2.5 to 12 g/cm³. Typically, the metal bondcomprises at least one metal selected from the group consisting of Ni,Fe, Co, Cu, and Sn, an alloy comprising at least two of the foregoingmetals, or an alloy comprising at least one of the foregoing metals andphosphorus.

As stated in the preamble, most outer blade cutting wheels used in theart for cutting rare earth sintered magnets are resinoid-bonded diamondcutting wheels having diamond abrasive grains bound with phenolic resinsor the like. For the purposes of improving the yield and reducing thecost of machining rare earth sintered magnets, it is desired to reducethe thickness of the peripheral blade section and to accelerate thecutting speed.

In efforts to meet these requirements, the inventors paid attention tothe bond used to bind abrasive grains to the periphery of a cementedcarbide base. The outer blade cutting wheel consists essentially of acemented carbide base as a base wheel and a blade section of boundabrasive grains. The blade section includes abrasive grains in the formof diamond grains, CBN grains or a mixture of diamond grains and CBNgrains, and a bond for binding the abrasive grains to the base. The bondfunctions to retain abrasive grains and to bind abrasive grains to thebase, so as to withstand the rotational force and the grindingresistance during cutting operation, thus accomplishing cutting ofworkpieces.

The form and role of bond are described. One important factor for thebond is that the blade section formed by the bond is disposed on theouter periphery of a base so as to straddle the outer rim of the base.The portion (or legs) of the blade section that straddles the outer rimof the base may be an abrasive layer of abrasive grains in admixturewith the bond or a layer of the bond alone, depending on the nature ofworkpiece material or a cutting purpose. Consequently, the thickness ofthe blade section is greater than that of the base. Such a shape istaken for two reasons. One reason is to increase the bond-base contactarea to achieve a firm engagement. If the blade section is configured soas to contact only the end face of the base, the bond is expected toachieve an insufficient bond strength to the base so that the bladesection will readily separate from the base. When the blade section isdisposed so as to straddle the base rim, the bond-base contact area isincreased to provide a sufficient bond strength between the base and thebond.

The other reason is to provide for ease of escape of grinding fluid andcutting sludge. The configuration of the blade section which is thickerthan the base means that there is a gap between the base and theworkpiece (typically magnet) at a position inside the blade section.This gap is very important in cutting operation because the grindingfluid will enter the gap which gives a passage for removing the heat offriction generated between the workpiece and the blade section andflowing away the grinding fluid with the swarf sludge entrained thereon.Absent the gap, swarf sludge as cut off will be captured or engagedbetween the blade section and the workpiece to cause substantialfriction, and the grinding fluid will not reach the blade tip, failingto release the heat of friction and to continue cutting operation.

The hardness of the bond is also important. As abrasive grains ofdiamond or CBN are rounded on their edges to increase cuttingresistance, the abrasive grains will shed under the external force. Atsites where abrasive grains have shed, the bond must be abraded by theworkpiece (rare earth sintered magnet) so that abrasive grains buriedunderneath may emerge from below. When abrasive grains shed or areabraded away, only the bond is left on the surface of the blade section,and the bond portion from which abrasive grains are lost must be scrapedoff. As the bond is scraped by the workpiece, new abrasive grains emergeby themselves from below. If this cycle is repeated, fresh sharp cuttingedges are automatically regenerated (known as “self-sharpening”).

The invention has succeeded in developing a high-performance outer bladecutting wheel by studying the characteristics required for the bond inthe blade section and tailoring the bond so as to meet the requirement.

Specifically, the mechanical nature of the bond used in the bladesection is improved to enhance the overall mechanical strength of theouter blade cutting wheel. In this way, a high-performance,high-strength cutting wheel is provided. While resin bonds of phenolicresins or the like are most commonly used in the art, they are scarcelyexpected to exert their own mechanical strength because of the resinousor plastic nature. According to the invention, a blade section is formedusing as the bond a single metal or metal alloy having excellentmechanical strength rather than the resins or plastics, whereby theblade section is improved in mechanical properties, and at the sametime, the strength of the base is reinforced. In this way, ahigh-performance outer blade cutting wheel with improved mechanicalrigidity or robustness is provided.

The patent references cited above, in part, refer to electrodepositionand metal bond, but not to necessary mechanical properties andconcomitant benefits. The mechanical strength of the blade section onthe outer periphery of the base is enhanced according to the inventionbecause the blade section comes in direct contact with the workpiece andmust be thicker than the base, and because the blade section is best forfacilitating mechanical reinforcement of the base. Enclosing the rim ofthe base with a thick metal material so as to reinforce the base is mosteffective in improving the mechanical properties of the whole base.

The outer blade cutting wheel of the invention is capable of cutting ata high accuracy and a reduced allowance, improves machining yields, andreduces machining costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an outer blade cutting wheel in oneembodiment of the invention, FIG. 1A being a plan view, FIG. 1B being across-sectional view taken along lines B-B in FIG. 1A, FIGS. 1C, 1D and1E being enlarged views of different examples of the blade section onthe base rim.

FIG. 2 is a photomicrograph of a blade section of agrain-co-electrodeposited outer blade cutting wheel in Example 1.

FIG. 3 is a diagram showing cutting accuracy versus cutting speed forExample 1 (grain-co-electrodeposited cutting wheel with an internalresidual stress of 0.53×10⁷ Pa), Example 2, Example 3, Example 4(grain-co-electrodeposited cutting wheel with an internal residualstress of 1.5×10⁸ Pa), Example 5 (grain-co-electrodeposited cuttingwheel with a Vickers hardness Hv of 440), Example 6, and ComparativeExample 1.

FIG. 4 is a diagram showing cutting accuracy versus elastic modulus(Young's modulus) for Examples 1 to 6 and Comparative Examples 1 and 2.

FIG. 5 is a diagram showing cutting accuracy versus Vickers hardness forExamples 1 to 6 and Comparative Examples 1 and 2.

FIG. 6 is a diagram showing cutting accuracy versus internal stress forExamples 1 to 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the outer blade cutting wheel in one embodiment ofthe invention is illustrated as comprising a base 10 in the form of anannular thin disc made of cemented carbide and a blade section 20disposed on the outer periphery of the base 10. The blade section 20comprises abrasive grains bound with a metal bond, the abrasive grainscomprising diamond grains, CBN grains or a mixture of diamond grains andCBN grains.

The base 10 is in the form of an annular thin disc (differently stated,a doughnut-shaped thin plate or circular thin plate having a center bore12) having an outer diameter of 80 to 200 mm, preferably 100 to 180 mm,defining an outer periphery, an inner diameter of 30 to 80 mm,preferably 40 to 70 mm, defining the bore 12, and a thickness of 0.1 to1.0 mm, preferably 0.2 to 0.8 mm.

It is noted that the disc has a center bore and an outer circumferenceas shown in FIG. 1. Thus, the terms “radial” and “axial” are usedrelative to the center of the disc, and so, the thickness is an axialdimension, and the length (or height) is a radial dimension.

Examples of the cemented carbide of which the base is made include thosein which powder carbides of metals in Groups IVB, VB, and VIB of thePeriodic Table such as WC, TiC, MoC, NbC, TaC and Cr₃C₂ are cemented ina binder matrix of Fe, Co, Ni, Mo, Cu, Pb, Sn or a metal alloy thereof,by sintering. Among these, typical WC—Co, WC—Ti, C—Co, and WC—TiC—TaC—Cosystems are preferred. Also, those cemented carbides which have anelectric conductivity sufficient to electroplating or which can be givensuch an electric conductivity with palladium catalysts or the like arepreferred. When cemented carbides are given an electric conductivitywith palladium catalysts or the like, well-known agents such asconductive treating agents used in plating of ABS resins may beemployed.

In the invention, the metal bond is used to form the blade section 20.The metal bond should have a Young's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa,and preferably 0.8×10¹¹ to 3.6×10¹¹ Pa. If the metal bond has a Young'smodulus of less than 0.7×10¹¹ Pa, the blade section can be deflected bythe cutting resistance that it receives during high-speed cutting,resulting in the cutting face being warped or undulated. If the metalbond has a Young's modulus of more than 4.0×10¹¹ Pa, the blade sectionis little deformed like the base, which is preferable for high accuracycutting; however, the metal bond has a higher hardness at the same timeso that when abrasive grains are abraded away or shed, self-sharpeningof a cutting edge does not occur for the above-described reason,resulting in a decline of cutting performance.

It is noted that the Young's modulus is determined by molding the bondalone into a part of suitable dimensions, working the part into aspecimen of measurement dimensions, placing the specimen in a thermostatchamber, and measuring by the resonance method.

The metal bond used herein preferably has a Vickers hardness of 100 to550 and a density of 2.5 to 12 g/cm³. A choice of hardness is made inconsideration of rare earth sintered magnets having a Vickers hardnessof about 600 to about 800. If the blade section is formed using the bondhaving a lower hardness than the workpiece or rare earth sinteredmagnet, the bond can be abraded by the workpiece when necessary,facilitating self-sharpening or self-emergence of abrasive grains. Withrespect to the density of metal bond which is correlated to Vickershardness, if the density is less than 2.5 g/cm³ and hence, lower thanthat of diamond and CBN, the bond may be low in strength to bindabrasive grains, allowing abrasive grains to shed. If the density ismore than 12 g/cm³ and hence, equal to or greater than that of cementedcarbide of which the base is made, the blade section may have a lowerbinding strength and become susceptible to chipping and shedding.

Vickers hardness is measured by a commercially available micro-Vickershardness tester because a specimen is so thin that the influence ofthickness must be minimized.

The metal bond used herein is at least one metal selected from the groupconsisting of Ni, Fe, Co, Cu, and Sn, an alloy comprising at least twoof the foregoing metals, or an alloy comprising at least one of theforegoing metals and phosphorus.

The abrasive grains used herein are diamond grains (including naturaldiamond and industrial synthetic diamond), cubic boron nitride (CBN)grains, or a mixture of diamond grains and CBN grains.

The size of abrasive grains depends on the thickness of the base towhich abrasive grains are bound. Preferably abrasive grains have anaverage particle size of 10 to 500 μm. If the average particle size isless than 10 μm, there may be left smaller gaps between abrasive grains,allowing problems like glazing and loading to occur during the cuttingoperation and losing the cutting ability. If the average particle sizeis more than 500 μm, there may arise problems, for example, magnetpieces cut thereby may have rough surfaces.

Preferably the blade section 20 contains abrasive grains in a fractionof 10 to 80% by volume, and more preferably 15 to 75% by volume. Lessthan 10 vol % means a less fraction of abrasive grains contributing tocutting whereas more than 80 vol % of abrasive grains may increaseunwanted loading during the cutting operation. Either situationincreases resistance during the cutting operation and so the cuttingspeed must be reduced. Depending on a particular application, the volumefraction of abrasive grains is controlled by admixing a suitableingredient other than abrasive grains.

As shown in FIGS. 1C to 1E, the blade section 20 consists of a pair ofclamp legs 22 a, 22 b which clamp the outer rim of the base 10therebetween in an axial direction and a body 28 which extends radiallyoutward beyond the outer rim (periphery) of the base 10. (This divisionis for convenience of description because the legs and the body areintegral to form the blade section.) The thickness of the blade section20 is greater than the thickness of the base 10.

More specifically, the clamp legs 22 a, 22 b of the blade section 20which clamp the outer rim of the base 10 therebetween each preferablyhave a length H1 of 0.1 to 10 mm, and more preferably 0.5 to 5 mm. Thelegs 22 a, 22 b each preferably have a thickness T3 of at least 5 μm(=0.005 mm), more preferably 5 to 2,000 μm, and even more preferably 10to 1,000 μm. Then the total thickness of legs 22 a, 22 b is preferablyat least 0.01 mm, more preferably 0.01 to 4 mm, and even more preferably0.02 to 2 mm. The blade section 20 is thicker than the base 10 by thistotal thickness. If the length H1 of clamp legs 22 a, 22 b is less than0.1 mm, they are still effective for preventing the rim of the cementedcarbide base from being chipped or cracked, but less effective forreinforcing the base and sometimes fail to prevent the base from beingdeformed by the cutting resistance. If the length H1 exceeds 10 mm,reinforcement of the base is made at the sacrifice of expense. If thethickness T3 of clamp leg is less than 5 μm, such thin legs may fail toenhance the mechanical strength of the base or to effectively dischargethe swarf sludge.

The base may be chamfered or notched at its outer peripheral region forthe purposes of preventing fracture and cracking during the cuttingoperation and enhancing electroplated strength. A proper mode ofchamfering such as C-chamfering or R-chamfering may be selected inaccordance with a particular situation. Also notches may be selectedfrom triangular and rectangular depressions and other shapes, dependingon parameters such as base thickness and abrasive layer height.

As shown in FIGS. 1C to 1E, the clamp legs 22 a, 22 b may consist of ametal bond 24 and abrasive grains 26 (FIG. 1C), consist of metal bond 24(FIG. 1D), or include an underlying layer consisting of metal bond 24covering the base 10 and an overlying layer consisting of metal bond 24and abrasive grains 26 (FIG. 1E).

On the other hand, the body 28 which extends radially outward beyond theperiphery of the base 10 has a length H2 which is preferably 0.1 to 10mm, and more preferably 0.3 to 8 mm, though may vary with the size ofabrasive grains to be bound. If the body length H2 is less than 0.1 mm,the blade section may be consumed within a short time by impacts andwears during the cutting operation, leading to a cutting wheel with ashort lifetime. If the body length H2 exceeds 10 mm, the blade sectionmay become susceptible to deformation, though dependent on the bladethickness (T2 in FIG. 1), resulting in cut magnet pieces with wavy cutsurfaces and hence, worsening dimensional accuracy. The body 28 of theblade section consists essentially of metal bond 24 and abrasive grains26.

The method of forming the blade section 20 on the periphery of the base10 may be either electroplating or brazing. By electroplating orbrazing, at least one metal selected from Ni, Fe, Co, Cu, and Sn, analloy thereof, or an alloy of such a metal with P is deposited on thecemented carbide base while binding abrasive grains therewith.

The method of depositing the metal bond by plating is generallyclassified into two, an electroplating method and an electroless platingmethod. In the practice of the invention, the electroplating method isselected at the present because it is easy to control internal stressesremaining in the metal bond and needs low production costs.

Electroplating may be carried out by any well-known technique using awell-known electroplating bath for depositing the above-listed singlemetal or alloy and ordinary plating conditions commonly used for thatbath.

When the metal bond is deposited by electroplating, abrasive grains mustbe bonded together and bound to the base by the metal bond at the sametime. This may be achieved by a composite plating method using acomposite plating bath having abrasive grains dispersed therein forco-depositing abrasive grains simultaneous with metal deposition as wellas the following methods.

(i) Method of applying a conductive adhesive to a selected portion ofthe base rim and bonding abrasive grains thereto with the adhesive,followed by plating.

(ii) Method of applying a mixture of a conductive adhesive and abrasivegrains to a selected portion of the base rim, followed by plating.

(iii) Method of clamping the base with a jig provided with a narrowspace corresponding to an abrasive layer, filling the space withabrasive grains, and causing friction forces to be generated amongabrasive grains, the jig and the base to retain the abrasive grains,followed by plating.

(iv) Method of cladding abrasive grains with a magnetic material such asnickel via plating or sputtering, and holding the clad grains to thebase rim via magnetic attraction, followed by plating. Means of inducingmagnetic forces through the base may be one known from JP-A 7-207254 orby clamping the base with a jig having a permanent magnet built therein.

(v) Method of cladding abrasive grains with a ductile metal such asnickel or copper, optionally mixing the clad grains with a metal powder,placing the clad grains alone or the clad grains/metal powder mixture onthe base rim, placing in a mold, and applying pressure for bonding.

It is noted that abrasive grains may be previously coated (or clad) byelectroless copper or nickel plating in order to increase the bondstrength of abrasive grains bonded by subsequent plating.

In the practice of the invention, when the metal bond is deposited bythe electroplating method, the metal as deposited should preferably havea stress between −2×10⁸ Pa (compression stress) and +2×10⁸ Pa (tensilestress), and more preferably between −1.8×10⁸ Pa and +1.8×10⁸ Pa. It isdifficult to measure directly the stress introduced in the base byelectroplating. Then, the metal is deposited on a test piece (e.g., atest strip used in commercial strip electrodeposit stress meters or atest piece used in internal stress measurement by a spiralcontractometer) under the same conditions as the plating conditionsunder which the metal is deposited on the base rim, before the stress ofthe plating film is measured. These data are compared with the resultsof a cutting test as in Example, and an appropriate range of stress inthe plating film is determined. As a consequence, a stress is found tofall in the range between −2×10⁸ Pa and +2×10⁸ Pa, provided thatnegative values represent the compression stress and positive valuesrepresent the tensile stress in the plating film. If a plating film hasa stress outside the range, the blade section or cemented carbide basemay be deformed by the stress, or deformation by the cutting resistancemay readily occur. As used herein, the term “stress” in a plating filmrefers to the internal stress which is left, when a plating film on anobject expands or contracts, as a result of expansion or contraction ofthe plating film being suppressed by the object to be plated.

The stress in the plating film may be controlled by suitable means. Forexample, in single metal plating such as copper or nickel plating,typically nickel sulfamate plating, the stress may be controlled byselecting the concentration of the active ingredient or nickelsulfamate, the current density during plating, and the temperature ofthe plating bath in appropriate ranges, and adding an organic additivesuch as o-benzenesulfonimide or p-toluenesulfonamide, or an element suchas Zn or S. Besides, in alloy plating such as Ni—Fe alloy, Ni—Mn alloy,Ni—P alloy, Ni—Co alloy or Ni—Sn alloy, the stress may be controlled byselecting the content of Fe, Mn, P, Co or Sn in the alloy, thetemperature of the plating bath, and other parameters in appropriateranges. In the case of alloy plating, addition of organic additives may,of course, be effective for stress control.

Examples of the preferred plating bath are given below.

Nickel sulfamate plating bath Nickel sulfamate 100-600 g/L Nickelsulfate  50-250 g/L Nickel chloride   5-70 g/L Boric acid  30-40 g/Lo-Benzenesulfonimide appropriate Nickel-cobalt alloy sulfamate platingbath Nickel sulfamate 250-600 g/L Cobalt chloride   2-10 g/L Boric acid 30-40 g/L o-Benzenesulfonimide appropriate Watts nickel-iron alloyplating bath Nickel sulfate  50-200 g/L Nickel chloride  20-100 g/L Ironsulfate   5-20 g/L Boric acid  30-40 g/L Sodium ascorbate appropriateo-Benzenesulfonimide appropriate Watts nickel-phosphorus alloy platingbath Nickel sulfate  50-200 g/L Nickel chloride  20-100 g/LOrtho-phosphoric acid  10-80 g/L Phosphorous acid   1-30 g/Lo-Benzenesulfonimide appropriate Copper pyrophosphate plating bathCopper pyrophosphate  30-150 g/L Potassium pyrophosphate 100-450 g/LAqueous ammonia   1-20 ml/L Potassium nitrate   5-20 g/L

In the other embodiment, the blade section is formed by brazing abrasivegrains with a metal bond onto the base rim. This may be carried out bypremixing a braze with abrasive grains and applying the premix to thebase rim or by premixing a braze with abrasive grains and placing thepremix and the base in a mold and applying pressure to bind the abrasivegrains to the base rim. Further, the metal bond may be deposited on thebase periphery by electroplating, to form an undercoat capable offacilitating subsequent brazing, for the purposes of enhancing the bondstrength between the abrasive layer and the base and substantiallypreventing the base from being deflected or waved by strains associatedwith brazing.

The braze used herein must have good wetting properties to cementedcarbides. Those braze materials having a melting point of up to 1,300°C., especially up to 1,100° C. are preferred because the deformation andstrength loss of the base are minimized.

Either of the above embodiments facilitates both the attachment ofdiamond grains, CBN grains or a mixture of diamond grains and CBN grainsto the periphery of the base and the enhancement of mechanical strengthof the thin base at the same time. The preferred dimensions of the baseinclude a thickness of 0.1 to 1 mm and an outer diameter of up to 200mm, because a base blank can be machined to such dimensions at a highaccuracy and the resulting wheel can be used to cut rare earth sinteredmagnet blocks at a high accuracy over a long term in a stable manner. Itis difficult to machine out a base disc of less than 0.1 mm thick at ahigh accuracy, because such an extremely thin disc experiencessubstantial axial curvatures independent of its outer diameter. Athickness in excess of 1 mm leads to an unacceptable cutting cost,failing to achieve the object of the invention. The outer diameter of upto 200 mm is due to the limitation of the current cemented carbidemanufacturing and machining technology. The diameter of the central boreis in the range of 30 to 80 mm which corresponds to the diameter of ashaft of a grinding machine on which the cutting wheel is mounted.

On use of the outer blade cutting wheel of the invention, variousworkpieces may be cut thereby. Typical workpieces include R—Co rareearth sintered magnets and R—Fe—B rare earth sintered magnets wherein Ris at least one of rare earth elements inclusive of Y. These magnets areprepared as follows.

R—Co rare earth sintered magnets include RCo₅ and R₂Co₁₇ systems. Ofthese, the R₂Co₁₇ magnets have a composition (in % by weight) comprising20-28% R, 5-30% Fe, 3-10% Cu, 1-5% Zr, and the balance of Co. They areprepared by weighing source materials in such a ratio, melting them,casting the melt, and finely pulverizing the alloy into an averageparticle size of 1-20 μm, yielding a R₂Co₁₇ magnet powder. The powder isthen compacted in a magnetic field and sintered at 1,100-1,250° C. for0.5-5 hours, followed by solution treatment at a temperature lower thanthe sintering temperature by 0-50° C. for 0.5-5 hours, and agingtreatment of holding at 700-950° C. for a certain time and subsequentcooling.

R—Fe—B rare earth sintered magnets have a composition (in % by weight)comprising 5-40% R, 50-90% Fe, and 0.2-8% B. An additive element orelements may be added thereto for improving magnetic properties andcorrosion resistance, the additive elements being selected from C, Al,Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta, W,etc. The amount of additive element is up to 30% by weight for Co, andup to 8% by weight for the other elements. The magnets are prepared byweighing source materials in such a ratio, melting them, casting themelt, and finely pulverizing the alloy into an average particle size of1-20 μm, yielding a R—Fe—B magnet powder. The powder is then compactedin a magnetic field and sintered at 1,000-1,200° C. for 0.5-5 hours,followed by aging treatment of holding at 400-1,000° C. for a certaintime and subsequent cooling.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation.

In Examples, the Young's modulus, Vickers hardness and plating stress ofa metal bond are measured by the following methods.

Young's Modulus

A metal bond was deposited on a cemented carbide base to a thickness ofabout 2 mm. The bond deposit was peeled therefrom and machined into aspecimen of 10×40×1 mm (thick). The Young's modulus of the specimen wasmeasured according to the bending resonance method of JIS R1605.

Vickers Hardness

The Vickers hardness of the specimen prepared above was measured by amicro-Vickers hardness tester according to the Vickers hardness test ofJIS 81610.

Plating Stress

A metal bond was deposited on a test strip (used in strip electrodepositstress meters) to a thickness of about 50 μm, after which a platingstress was measured.

Example 1

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Inaccordance with method (iv) mentioned above, nickel-clad diamond grainshaving an average particle size of 130 μm were disposed in contact withthe periphery of the base. The base was immersed in a nickel sulfamateplating bath at 50° C. where a different quantity of electricity wasconducted at a current density of 5 to 20 A/dm² for electroplating.After water washing and removal from the jig, a blade section was lappedby a lapping machine to a thickness of 0.4 mm. In this way, there wereobtained three types of outer blade cutting wheels with abrasive grainsbound by electroplating, having a different internal residual stress.FIG. 2 is a photomicrograph showing the outer appearance of the bladesection having the cross section shown in FIG. 1D. Illustrated in FIG. 2are a cemented carbide base 10, a layer (leg) of metal bond 24, and alayer (body) of metal bond 24 and abrasive grains 26. The metal bondshad a Young's modulus of 2.0×10¹¹ Pa, a Vickers hardness of Hv 318, adensity of 8.8 g/cm³, and an internal residual stress of −1.4×10⁸ Pa,0.53×10⁸ Pa, and 2.0×10⁸ Pa.

Example 2

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Inaccordance with method (iv) mentioned above, nickel-clad CBN grainshaving an average particle size of 130 μm were disposed in contact withthe periphery of the base. The base was immersed in a nickel sulfamateplating bath at 50° C. where electricity was conducted at a currentdensity of 5 to 20 A/dm² for electroplating. After water washing andremoval from the jig, a blade section was lapped by a lapping machine toa thickness of 0.4 mm. In this way, there was obtained an outer bladecutting wheel with abrasive grains bound by electroplating. The metalbond had a Young's modulus of 2.0×10¹¹ Pa, a Vickers hardness of Hv 318,a density of 8.8 g/cm³, and an internal residual stress of 0.5×10⁸ Pa.

Example 3

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Asin Example 1, nickel-clad diamond grains having an average particle sizeof 130 μm were disposed in contact with the periphery of the base. Thebase was immersed in a nickel-cobalt alloy sulfamate plating bath at 50°C. where electricity was conducted at a current density of 5 to 20 A/dm²for electroplating. After water washing and removal from the jig, ablade section was lapped by a lapping machine to a thickness of 0.4 mm.In this way, there was obtained an outer blade cutting wheel withabrasive grains bound by electroplating. The metal bond had a Young'smodulus of 2.4×10¹¹ Pa, a Vickers hardness of Hv 480, a density of 8.8g/cm³, and an internal residual stress of 4.6×10⁷ Pa.

Example 4

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Asin Example 1, nickel-clad diamond grains having an average particle sizeof 130 μm were disposed in contact with the periphery of the base. Thebase was immersed in a Watts nickel-iron alloy plating bath at 60° C.where a different quantity of electricity was conducted at a currentdensity of 5 to 20 A/dm² for electroplating. After water washing andremoval from the jig, a blade section was lapped by a lapping machine toa thickness of 0.4 mm. In this way, there were obtained two types ofouter blade cutting wheels with abrasive grains bound by electroplating,having a different internal residual stress. The metal bonds had aYoung's modulus of 1.4×10¹¹ Pa, a Vickers hardness of Hv 422, a densityof 8.7 g/cm³, and an internal residual stress of −0.5×10⁸ Pa and 1.5×10⁸Pa.

Example 5

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Asin Example 1, nickel-clad diamond grains having an average particle sizeof 130 μm were disposed in contact with the periphery of the base. Thebase was immersed in a Watts nickel-phosphorus alloy plating bath of adifferent composition at 60° C. where electricity was conducted at acurrent density of 5 to 20 A/dm² for electroplating. After water washingand removal from the jig, a blade section was lapped by a lappingmachine to a thickness of 0.4 mm. In this way, there were obtained twotypes of outer blade cutting wheels with abrasive grains bound byelectroplating, having a different Vickers hardness. The metal bonds hada Young's modulus of 2.1×10¹¹ Pa, a Vickers hardness of Hv 440 and Hv528, a density of 8.8 g/cm³, and an internal residual stress of 0.9×10⁷Pa.

Example 6

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was masked with adhesive tape so that only a circumferentialregion of either surface extending 1.5 mm inward from the outerperiphery was exposed. The base was immersed in a commercially availableaqueous alkaline solution at 40° C. for 10 minutes for degreasing,washed with water, and immersed in an aqueous solution of 30 to 80 g/Lof sodium pyrophosphate at 50° C. where electrolysis was effected at acurrent density of 2 to 8 A/dm². The cemented carbide base wasultrasonic washed in deionized water and held by a jig for plating. Asin Example 1, nickel-clad diamond grains having an average particle sizeof 130 μm were disposed in contact with the periphery of the base. Thebase was immersed in a copper pyrophosphate plating bath at 50° C. whereelectricity was conducted at a current density of 5 to 20 A/dm² forelectroplating. After water washing and removal from the jig, a bladesection was lapped by a lapping machine to a thickness of 0.4 mm. Inthis way, there was obtained an outer blade cutting wheel with abrasivegrains bound by electroplating. The metal bond had a Young's modulus of1.1×10¹¹ Pa, a Vickers hardness of Hv 150, a density of 8.8 g/cm³, andan internal residual stress of 0.5×10⁷ Pa.

All the cutting wheels of Examples 1 to 6 were suited for cutting rareearth sintered magnet blocks.

Comparative Example 1

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was placed in a mold, which was filled with a mixture of 75% byvolume of a powdered phenolic resin as a resin bond and 25% by volume ofdiamond grains having an average particle size of 130 μm. The mixturewas pressure molded about the base and heated in the mold at 180° C. for2 hours for curing. After cooling and removal from the mold, a bladesection was lapped by a lapping machine to a thickness of 0.4 mm. Inthis way, there was obtained a resin bonded cemented carbide outer bladecutting wheel. The bond had a Young's modulus of 3.0×10⁹ Pa, a Vickershardness of Hv 50, and a density of 4.3 g/cm³.

Comparative Example 2

A cemented carbide consisting of 90 wt % WC and 10 wt % Co was machinedinto an annular thin disc having an outer diameter of 125 mm, an innerdiameter of 40 mm, and a thickness of 0.3 mm, which served as a base.The base was placed in a mold, which was filled with a mixture of 75% byvolume of a WC powder/Co powder mix as a bond and 25% by volume ofdiamond grains having an average particle size of 130 μm. Pressuremolding was performed. The base was removed from the mold, followed bythickness adjustment and heat treatment in an argon atmosphere. A bladesection was lapped by a lapping machine to a thickness of 0.4 mm. Inthis way, there was obtained a sintered, cemented carbide base outerblade cutting wheel. The bond had a Young's modulus of 5.1×10¹¹ Pa, aVickers hardness of Hv 687, and a density of 13.1 g/cm³.

A cutting test was performed. A multiple wheel assembly was constructedby arranging two outer blade cutting wheels from each of Examples 1 to 6and Comparative Examples 1 and 2 at a spacing of 1.5 mm. The assemblywas dressed until abrasive grains became exposing. A number ofworkpieces in the form of Nd—Fe—B rare earth sintered magnet of 40 mmwide×100 mm long×20 mm high were successively cut by the assembly whilerotating the assembly at 5,000 rpm.

FIG. 3 is a diagram illustrating a cutting accuracy versus a cuttingspeed. After 50 magnet pieces were cut from the start at a cutting speedof 10 mm/min, five magnet pieces were cut while varying a cutting speedfrom 10 mm/min to 35 mm/min. For each piece, the thickness at fivepoints, a central point and four corner points was measured by amicro-meter. The difference between maximum and minimum values amongthese five points for each piece is a cutting accuracy (μm). An averageof the cutting accuracies of five pieces was computed and plotted in thediagram.

FIGS. 4, 5, and 6 are diagrams illustrating a cutting accuracy versus anelastic modulus (Young's modulus), Vickers hardness, and internalstress, respectively. For each of five magnet pieces cut at a speed of30 mm/min, the thickness at five points, a central point and four cornerpoints was measured by a micro-meter. The difference between maximum andminimum values among these five points for each piece is a cuttingaccuracy (μm). An average of the cutting accuracies of five pieces wascomputed and plotted in the diagrams.

FIG. 3 illustrates a cutting accuracy versus a cutting speed forExamples 1 to 6 and Comparative Example 1. In Comparative Example 1, asthe cutting speed increases, the cutting accuracy increasessubstantially. In Examples, the cutting accuracy is less than 60 μm forall samples, despite more or less magnitudes of difference, indicatingthat the dimensional variation is minimized even on high speed cutting.

FIG. 4 illustrates a cutting accuracy versus an elastic modulus (Young'smodulus) of bond for Examples 1 to 6 and Comparative Examples 1 and 2.Comparative Example 1 had a cutting accuracy above 150 μm andComparative Example 2 had a cutting accuracy approximate to 250 μm, bothexceeding the acceptable cutting accuracy of 100 μm. In contrast,Examples 1 to 6 had satisfactory cutting accuracy values of less than100 μm. The dotted line curve in the diagram is a regression curvecalculated from these data, and it is estimated from the regressioncurve that the range of Young's modulus providing an acceptable cuttingaccuracy is between 0.7×10¹¹ Pa and 4.0×10¹¹ Pa.

FIG. 5 illustrates a cutting accuracy versus an Vickers hardness of bondfor Examples 1 to 6 and Comparative Examples 1 and 2. ComparativeExample 1 had a cutting accuracy above 150 μm. In contrast, Examples 1to 6 had satisfactory cutting accuracy values of less than 100 μm,indicating satisfactory dimensional variations. The dotted line curve inthe diagram is a regression curve calculated from these data, and it isestimated from the regression curve that the range of Vickers hardnessproviding a cutting accuracy of up to 100 μm is between Hv 100 and Hv550.

FIG. 6 illustrates a cutting accuracy versus an internal stress of bondfor Examples 1 to 6. It is estimated from the regression curve in thediagram that the range of internal stress providing a cutting accuracyof up to 100 μm is between −2.0×10⁸ Pa and 2.0×10⁸ Pa.

It has been demonstrated that according to the invention, the bladesection is improved in mechanical strength and the overall outer bladecutting wheel is improved in mechanical rigidity or robustness. As aresult, even when the thickness of the blade section is reduced, theconcomitant reduction of cutting accuracy during high-speed cutting isminimized.

Japanese Patent Application No. 2007-339212 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A method for preparing an outer bladecutting wheel comprising providing a base in the form of an annular thindisc of cemented carbide having an outer diameter of 80 to 200 mmdefining an outer periphery, an inner diameter of 30 to 80 mm, and athickness of 0.1 to 1.0 mm, forming an undercoat consisting of a metalbond on an outer periphery of the base in such a manner that the outerperiphery of the base is sandwiched between portions of the undercoat ina thickness direction of the base, the undercoat being formed byelectroplating, and after forming the undercoat, brazing abrasive grainswith the metal bond onto the undercoat to form a layer in which theabrasive grains are bound with the metal bond, so as to form a bladesection, wherein: the blade section has a pair of clamp portions and abody, each of the pair of clamp portions comprises an overlying layerconsisting of the abrasive grains and the metal bond on one of theportions of the undercoat sandwiching the outer periphery of the base inthe thickness direction of the base, the body extends radially outwardbeyond the outer periphery of the base, the body consisting of theabrasive grains and the metal bond, the abrasive grains comprise diamondgrains, CBN grains or a mixture of diamond grains and CBN grains, themetal bond having a Young's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa, theblade section has a thickness which is greater than the thickness ofsaid base by at least 0.01 mm, the metal bond binds the abrasive grainsto the outer periphery of the base and comprises: an alloy consisting ofNi and Co; an alloy consisting of Ni and Co, and at least one elementselected from the group consisting of Zn, S and Fe; an alloy consistingof Ni and phosphorus; or an alloy consisting of Ni, phosphorus, and atleast one element selected from the group consisting of Zn, S and Fe. 2.The method of claim 1 wherein said metal bond has a Vickers hardness of100 to 550 and a density of 2.5 to 12 g/cm³.
 3. The method of claim 1wherein the abrasive grains are clad with a magnetic material formed byplating or sputtering, or a ductile metal.
 4. The method of claim 1wherein said metal bond comprises an alloy consisting of Ni andphosphorus.
 5. The method of claim 1 wherein prior to said brazing, theabrasive grains are at least one of the group consisting of: clad byelectroless copper plating and clad by electroless nickel plating.
 6. Amethod for preparing an outer blade cutting wheel comprising providing abase in the form of an annular thin disc of cemented carbide having anouter diameter of 80 to 200 mm defining an outer periphery, an innerdiameter of 30 to 80 mm, and a thickness of 0.1 to 1.0 mm, forming anundercoat consisting of a metal bond on an outer periphery of the basein such a manner that the outer periphery of the base is sandwichedbetween portions of the undercoat in a thickness direction of the base,the undercoat being formed by electroplating, and after forming theundercoat, brazing abrasive grains with the metal bond onto theundercoat to form a layer in which the abrasive grains are bound withthe metal bond, so as to form a blade section, wherein: the bladesection has a pair of clamp portions and a body, each of the pair ofclamp portions comprises an overlying layer consisting of the abrasivegrains and the metal bond on one of the portions of the undercoatsandwiching the outer periphery of the base in the thickness directionof the base, the body extends radially outward beyond the outerperiphery of the base, the body consisting of the abrasive grains andthe metal bond, the abrasive grains comprise diamond grains, CBN grainsor a mixture of diamond grains and CBN grains, the metal bond having aYoung's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa, the blade section has athickness which is greater than the thickness of said base by at least0.01 mm, the metal bond binds the abrasive grains to the outer peripheryof the base and comprises: an alloy consisting of Ni, at least one metalselected from the group consisting of Fe, Cu and Sn, and; an alloyconsisting of Ni, at least one metal selected from the group consistingof Fe, Cu and Sn, and Zn and S; an alloy consisting of Ni—Mn, and S; oran alloy consisting of Ni—Mn, at least one metal selected from the groupconsisting of Zn and Fe, and S.
 7. The method of claim 6 wherein saidmetal bond has a Vickers hardness of 100 to 550 and a density of 2.5 to12 g/cm³.
 8. The method of claim 6 wherein the abrasive grains are cladwith a magnetic material formed by plating or sputtering, or a ductilemetal.
 9. The method of claim 6 wherein prior to said brazing, theabrasive grains are at least one of the group consisting of: clad byelectroless copper plating and clad by electroless nickel plating.
 10. Amethod for preparing an outer blade cutting wheel comprising providing abase in the form of an annular thin disc of cemented carbide having anouter diameter of 80 to 200 mm defining an outer periphery, an innerdiameter of 30 to 80 mm, and a thickness of 0.1 to 1.0 mm, forming anundercoat consisting of a metal bond on an outer periphery of the basein such a manner that the outer periphery of the base is sandwichedbetween portions of the undercoat in a thickness direction of the base,the undercoat being formed by electroplating, and after forming theundercoat, brazing abrasive grains with the metal bond onto theundercoat to form a layer in which the abrasive grains are bound withthe metal bond, so as to form a blade section, wherein: the bladesection has a pair of clamp portions and a body, each of the pair ofclamp portions comprises an overlying layer consisting of the abrasivegrains and the metal bond on one of the portions of the undercoatsandwiching the outer periphery of the base in the thickness directionof the base, the body extends radially outward beyond the outerperiphery of the base, the body consisting of the abrasive grains andthe metal bond, the undercoat is at least as thick as the overlyinglayer, the abrasive grains comprise diamond grains, CBN grains or amixture of diamond grains and CBN grains, the metal bond having aYoung's modulus of 0.7×10¹¹ to 4.0×10¹¹ Pa, the blade section has athickness which is greater than the thickness of said base by at least0.01 mm, the metal bond binds the abrasive grains to the outer peripheryof the base and comprises: an alloy consisting of Ni and Co; an alloyconsisting of Ni and Co, and at least one element selected from thegroup consisting of Zn, S and Fe; an alloy consisting of Ni andphosphorus; or an alloy consisting of Ni, phosphorus, and at least oneelement selected from the group consisting of Zn, S and Fe.